1. Field of the Invention
The present invention relates to a focusing apparatus. More particularly, the present invention relates to a focusing apparatus for adjusting focus of optical instrument.
2. Description of the Related Art
Japanese Laid-Open Patent Application No. 10-293245 discloses an electronic camera which performs supplemental focusing with contrast focus control means after performing focusing with a focus control means by external metering.
However, according to the above described conventional electronic camera, the contrast focus control means performs contrast detection by hill-climbing method, where the contrast focus control means measures contrast value from solid state image pick-up device like a CCD or a CMOS image sensor and finds out a focusing position on which the contrast value becomes a maximum value by gradually pushing out the optical unit. Since the contrast focus control means needs to move the optical unit for several times intermittently to perform the contrast detection by hill-climbing method, there is a problem that it takes time for the optical unit to reach the focusing position.
Therefore, it is an object of the present invention to provide a focusing apparatus, which is capable of overcoming the above drawbacks accompanying the conventional art. The above and other objects can be achieved by combinations described in the independent claims. The dependent claims define further advantageous and exemplary combinations of the present invention.
According to the first aspect of the present invention, a focusing apparatus for adjusting focus of an optical instrument including: an optical unit for acquiring light from a subject and forming a subject image; a contrast detecting unit for detecting contrast value of the subject image acquired by the optical unit; a distance measuring unit for computing distance information indicating a distance from the focusing apparatus to the subject; an adjustment command receiving unit for receiving command information indicating a request to adjust the focus of the optical unit; a focus control unit for performing contrast detection by hill-climbing method by acquiring a contrast value step-by-step by moving at least a part of the optical unit step-by-step, and detecting a position of the optical unit, where the acquired contrast value becomes a maximum values, as a focusing position, when the adjustment command receiving unit receives the command information; a difference information computing unit for computing difference information indicating the difference between the focusing position detected by the focus control unit, which performs the contrast detection by hill-climbing method, and an adjustment position of the optical unit corresponding to the distance information computed by the distance measuring unit; and a difference information storing unit for storing the difference information computed by the difference information computing unit, wherein the distance measuring unit newly computes distance information when the adjustment command receiving unit receives command information later, and the focus control unit determines a condition for the contrast detection by hill-climbing method on the basis of the difference information stored in the difference information storing unit and distance information newly computed by the distance measuring unit.
The focus control unit may determine width of an adjustment range of the optical unit, which performs the contrast detection by hill-climbing method, on the basis of the difference information stored in the difference information storing unit and the distance information newly computed by the distance measuring unit. Moreover, the focus control unit may determine a center of an adjustment range of the optical unit, which performs the contrast detection by hill-climbing method, on the basis of the difference information stored in the difference information storing unit and the distance information newly computed by the distance measuring unit.
The summary of the invention does not necessarily describe all necessary features of the present invention. The present invention may also be a sub-combination of the features described above.